I used to have an ED and I gained the most weight eating like you describe. (I'm 5'3'') I barely ate and when I ate a normal amount I gained..and didn't lose it when I returned to barely eating. That kind of behavior really, really messes up your metabolism. In fact, I realized my disordered eating was making me fat and that was what finally drove me to start eating more. I thought when I started eating 1,500 calories that I would gain tons of weight and that it would take forever to fix my metabolism but once you truly start eating enough on a regular basis it doesn't take that long for your metabolism to pick up. Once I got my metabolism up to speed (I continued to increase my calories above 1,500) I didn't try to lose weight for awhile. When I did, I cut my calories just a little and worked out with weights and the weight dropped off me without me being hungry! I like diets with calories spaced throughout the day and lots of fiber, healthy fats, lean proteins and some complex carbs. I suggest you see a doctor and a therapist. If they give you the go ahead you can begin lifting once you start eating regular amounts to build back muscle instead of fat. Remember, even if eating regular amounts causes you to gain a little-thats temporary. In the long run you will end up thinner and more toned by following a healthy meal plan and weight training program. (I suggest The New Rules of Lifting for Women). I ate just a tad less than what they recommend in that book and followed their lifting program and lost twenty pounds. Also, your second goal weight is really unhealthy sounding and scares me for you.

A bit about my diet:
Some people have issues overeating, I have issues undereating. I get busy throughout the day with my job and keep putting off meals. Then I get home and work out and watch some shows. If my bf isn't hungry I don't make dinner and end up just not eating. I eat about 300-500 calories a day. When I do get myself to eat though and eat somewhere around 800-1000 calories I end up gaining like 2lbs.
What I don't understand is that my body burns about 1500 calories a day and with the exercise another 500 are burned so I don't get how I can gain weight from 1000 calories. Yes i'm trying to fix my eating habits, but in the meantime i'm confused. Why would that make me gain so much weight?
I don't think it's my metabolism because I take fiber in the morning and evening and I drink icy cold water all day.
Thoughts??

first of all avoid drinking icy cold water as it slows metabolism instead drink little warm water it will increase matabolism, and yes its agood thing that you are taking fibre !!

change that cold water drinking habit and you will see the change in your lbs!!

Depends on how carefully you measure the food that you eat, how well you know what is in that food, and how faithfully you report all that you eat to a food log so you get a very accurate picture of what your caloric intake is.

Don't even try to guess offhand how many calories you expend in physical activity. It's difficult to be extremely accurate about that, nowhere near as accurate as knowing how many calories are in a bag of frozen berries that weigh X amount of ounces and have nutritional information on the package.

So, if you are very accurate about the measures of what goes in your mouth, then the estimate that you only eat 300-500 calories a day is way out of whack, requiring you to see a doctor. Even if you are 5 feet 4 inches tall.

Fitday (and other websites) have tools for you to put in your height and weight and activity level (underestimate, rather than overestimate, that level - to start, then you can tweak it much later on if necessary). You can find how many calories you need to maintain your current weight.

Two pounds of weight is not much. For some people, that's actually water weight when they eat a lot of salty food - and it goes away when they watch the salt in their diet. It goes away within days.

If none of the above are factors, then a frank discussion with your doctor is in order. Eat only all the food from bags (frozen food) or boxes (all the contents) and bring the bags and boxes as proof. The nutrition information is right on the bags and boxes. Show your doctor, and give the exact time period you cover eating those foods. Weigh in at the beginning of that time period, preferably right there at the doctor's office. Then weigh in at the time of the visit to discuss your problem. He can see the severity of your condition and put your mind at ease with information he can show you when he has results from blood tests.

Agreed. 500 cal burn for a work out? Typical 1 hour weight lifting work out burns 200 cal at most, an extreme one (all heavy weight full body power moves) burns 300 at most. Not saying your are lying but most people think they are burning A LOT more calories while working out then they are. 500 an hour calorie burn is what my personal trainer room mate burns in an hour doing nothing but full body power moves non stop for 45 min with no rest (yes he is a monster)... unless you are doing that.. i seriously doubt you are burning 500 a work out.

Eating disorders have the highest mortality rate of any mental illness--up to 40% by some estimates. Our community member Skinnywallflower has an ED.

While she's currently at a healthy weight, her stated goal weight is 100lbs, which would put her at a BMI of 17.2. Underweight is 18.5 and below.

Going to a doctor could save her life, and encouraging her to do so is good. Support and love are good.

Advice on how to lose more weight? NOT HELPFUL to the person with the ED. With the greatest of love and respect, I ask you to PLEASE STOP GIVING HER TIPS ON HOW TO LOSE MORE WEIGHT. That is triggering and destructive.

Skinnywallflower, you are a sweet and awesome person. Please take care of yourself and do whatever you need to stay alive and healthy.

This is a general Problem !!
You are unable to maintain the balance between calorie intake and calorie Burn!!
Just take some high calorie intake in Morning , and in evening take only Low calorie high in protein diet (like Egg whites and all ) .

This will fix the issue !!
weight gain may be because of food substance remains after bowel Movement , it causing saturation and due to this weight is increasing !!
for articles relating your issue you can go to Top Causes of Unexpected Weight Gain

Based on your height and weight, and assuming a body fat % of 17% (Just assuming.. I have no idea what your BF % is, but it is relatively arbitrary here) then you have a Basal Metabolic Rate of ≈ 1340 calories per day. Your BMR is the number of calories your body burns simply by existing and handling normal bodily functions such as breathing, heartbeat, brain activity, etc. This does not include any exercise you do.

If you regularly only eat 300-500 calories, the reason you're gaining weight when you eat more than that is because your body is essentially operating in starvation mode most of the time. This happens when it doesn't get enough calories to sustain its normal functions. Your body essentially down-regulates the production of certain hormones and intentionally slows your metabolism to keep you from starving to death.

Simplified, when you are in a calorie deficit, your body has to break down some of its own tissues and convert them into usable energy to keep you going. This is the fundamental concept behind losing fat: the law of energy balance. If you take in more calories than you burn, you'll gain weight (either fat or muscle, depending on a variety of factors). If you take in the same as you burn, you'll maintain weight (but not always lean body mass, again depending on a variety of factors). If you take in less calories than you burn, then you'll lose weight (either fat or lean muscle tissue).

Reducing your calories causes you to lose fat, but reducing them too much makes your body think it's starving. When your body thinks its starving it kicks in many different survival mechanisms. If you're spending most of your time in starvation mode, when you do consume extra calories, your body will intentionally store them as fat after it meets its energy needs (which are now lowered due to the starvation response from your restricted calories).

The other problem is that when you restrict calories too much, your body will start to catabolize your lean muscle tissue to use for energy, and also to lower your body's caloric needs.

Your lean body mass is what primarily comprises your Basal Metabolic Rate. Simply put, the more lean muscle tissue you have, the more calories your body needs just to exist. So when your body catabolizes its muscle tissue, its essentially lowering your BMR, meaning your daily calorie requirements are lowered. That makes it much more likely that the next time you eat a large amount of calories you will be in a caloric surplus.

Lets take a look at an example of what typically happens when you restrict your calories too much:

Assuming 119 lbs @ 17% body fat, you have approximately 99 lbs. of lean body mass. You starve yourself for two weeks, only eating 300-500 calories per day. When you weigh yourself at the beginning of the following week, you weight 115 lbs, a loss of 4 lbs. But because your body is in starvation mode, a very large percentage of that weight is likely from lean muscle tissue. Assuming 50% is from LBM, your lean body mass is now only 97 lbs. Now say you go out and eat a large pizza or something and are in a caloric excess, you might find that you skyrocket back up to 119 lbs. But most of that weight is either water weight or fat. So now, your weight is the same as it was two weeks ago, but because you've lost lean muscle tissue, your body fat % is now closer to 18%.. which in gives you a lower daily caloric need even though you're the same weight.

This is an over simplification for explanation purposes, but this is the reason why you are experiencing this.

The best way to fix this problem is to start some resistance training (weights workouts) and to fix your eating habits. There will probably be a rough patch for the first week or two where your body gets used to the increased calories, and starts to gain weight. It is important to keep at it though. Another important thing to remember is that, especially if you're performing resistance training, you will be building lean muscle tissue as well. So keep in mind that an increase in scale weight does not always mean an identical increase in body fat.

Ideally, you'll want to figure out what your total daily energy expenditure (TDEE) is for your weight and body fat %, and accounting for your energy levels. In order to lose body fat while retaining lean muscle tissue, reduce your calorie intake by about 15-20% of your TDEE. This will allow your body to operate in a caloric deficit without triggering your body's survival mode.

Figuring out your TDEE is pretty easy if you know your current weight and your current body fat percentage. You can estimate your body fat and get a semi-close approximate of your TDEE.

So if I eat 2888 calories / day, I'm in a daily calorie deficit of 510 calories. That is 3570 calories per week, or about 1 lb of body fat that I should be losing.

In regards to hapababy's comments.. there is a great formula for figuring out what your ideal weight is.. which is based on body composition, not scale weight. That is a much more effective, and healthy method of setting a goal weight for yourself. The formula is (Current Lean Body Mass) / 1 - (Desired Body Fat %). So for instance if you're 119 lbs right now at 20% body fat, which is considered to be 'lean' or slightly above average for women.. you have 95.2 lbs of lean body mass. Say your goal is 15% body fat (considered to be very lean and fit for women) then your ideal body weight should be:

95.2 / .85 = 112 lbs.

A goal weight of 100 lbs would give you a goal body fat percentage of 5%, which for women is practically impossible to obtain or maintain (pretty much for men as well).